Field of the Invention
The present invention concerns a torsional damper comprising at least two coaxial parts mounted to rotate relative to one another within a defined range of relative angular movement and circumferentially acting elastic means between said parts resisting such relative angular movement.
This type of torsional damper is normally incorporated in the design of a friction clutch, particularly for automotive vehicles, in which case one coaxial part comprises a friction disk designed to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automotive vehicle, whereas the other of said coaxial parts is carried on a hub designed to rotate with a second shaft, in practice a driven shaft, for example the gearbox input shaft in the case of an automotive vehicle.
This type of torsional damper is used to permit regulated transmission of rotational torque applied to one of its coaxial parts where the other or others are themselves subject to a rotational torque. It is thereby able to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automotive vehicle.
The present invention more particularly concerns the case in which one of the coaxial parts incorporates a hub disk whilst a second of said coaxial parts incorporates two annular guides, axially disposed one on each side of said hub disk, the annular guides being axially linked to one another by a ring which extends in the radial direction beyond the periphery of the hub disk.
French patent No. 72 16111 filed May 5, 1972 and published under No. 2 183 390 and French patent application filed Oct. 14, 1981 under No. 81 19298 disclosed such an arrangement. French patent application No. 81 19298 has been published under No. 2,514,446 on Apr. 15, 1983. Further, commonly assigned U.S. application Ser. No. 428,602, filed Sept. 30, 1982, claims priority from French patent application No. 81 19298.
The circumferentially acting elastic means between two coaxial parts of a torsional damper normally comprise helical springs disposed substantially tangentially relative to a circumference of the damper assembly. The ultimate possible range of relative angular movement between these two coaxial parts is therefore determined by the turns of at least certain of these springs approaching continuity.
This inevitably results in a certain limitation of the maximum torque which can be transmitted from one coaxial part to the other.
This torque passes through the springs with their turns approaching contiguity, and in this case these springs in which crushing stresses are combined with the elastic torsional stresses, are generally at the maximum of their mechanical capability.
To avoid such a limitation, and notably, since it is desirable for friction clutches to equip heavy industrial vehicles, to enable additional torque to pass from one coaxial part constituting such a friction clutch to the other after absorption of the maximum possible relative angular movement, it has been proposed to equip the hub disk at its periphery with radially projecting pins each individually engaged, with clearance, between two axial shoulders formed for this purpose in the ring axially linking together the two associated annular guides.
Such an arrangement, whereby the ultimate possible relative angular movement between the two coaxial parts is determined by the provision of a positive circumferential abutment engagement of the pins against the corresponding axially disposed shoulders of the associated ring, is disclosed in the abovementioned French patent No. 72 16111 and French patent application No. 81 19298.
In practice, the axial shoulders thus presented by the ring are formed by the edge of an indentation formed for this purpose in the ring.
This results in a weakening of this ring, as well as a certain complication in assembling the torsional damper, since this assembly procedure may involve an initially non-parallel presentation of the hub disk with respect to the ring, before said hub disk is straightened.
To overcome this problem, it has already been proposed in French patent application filed Oct. 14, 1981 under No. 81 19298, to offset radially the free edge of the ring, at the expense of increasing the complexity of the ring.
The object of the present invention is to provide an arrangement to obtain the required axially disposed shoulders on such a ring in a simple manner, the invention also offering further advantages.
More precisely, the object of the present invention is a torsional damper suitable for use in a friction clutch, particularly for automotive vehicles, comprising at least two coaxial parts, mounted to rotate relative to one another within a defined range of relative angular movement, and elastic means comprising one coaxial part incorporating a hub disk and a second coaxial part incorporating two annular guides, axially disposed one on each side of the hub disk, the annular guides being axially linked to one another by a ring which extends in the radial direction beyond the periphery of the hub disk, the hub disk being equipped at its periphery with radially projecting pins each individually engaged, with clearance, between two axial shoulders of the ring, at least one of the axial shoulders thus presented by the ring for each of the pins of the hub disk being formed by the edge of an indentation formed in the circumference of the ring by simple local deformation of the ring.
Through such an arrangement, the mechanical weakening to which the ring is subjected through the formation of the required axial shoulders is rendered minimal, since none of the material of the ring is lost.
In addition, since the axial shoulders thus formed by indentations in the ring are themselves radially offset with respect to the continuous part of the ring, it is no longer necessary for the free edge of the ring to be offset in the radial direction, to obtain an axial engagement of the hub disk in the ring. In addition, for the same total radial dimension, the hub disk may if required present a higher diameter between the axial shoulders of the ring, without altering the ease with which it engages axially in the ring.
Since according to the invention the formation of indentations in the ring inevitably involves work hardening of the material constituting the ring, this ring advantageously presents increased mechanical strength through each of the axial shoulders which it presents to provide a circumferential abutment for the pins of the associated hub disk.
If for attachment to the ring, one of the annular guides has at intervals around its periphery radially projecting lugs which can be engaged in openings made for this purpose on the corresponding edge of the ring to secure the assembly, the axial shoulders of the ring may advantageously be circumferentially disposed on each side of these openings.
U.S. Pat. No. 2,210,074 discloses a torsional damper in which the axial shoulders presented by the ring for cooperation with the hub disk are formed by means of indentations therein.
However, unlike the arrangement disclosed by the present invention, the hub disk in U.S. Pat. No. 2,210,074 does not incorporate projecting pins for engagement between two indentations in the ring, but hollow openings in each of which it is engaged on a single such indentation.
This results in both a weakening of the mechanical strength of the hub disk, which is not circularly continuous at its periphery, since it incorporates openings, as well as a weakening of the mechanical strength of the ring since the deformation of the parts of the ring involved must be sufficient to be able to penetrate into the openings in the hub disk.
In practice, according to U.S. Pat. No. 2,210,074, the deformations in the ring corresponding to these indentations, in order to be radially sufficiently deep, affect the entire width of the ring.
In other words, the material of the ring is not axially continuous through these deformations, by virtue of the complete absence of material here.
This is not the case in the torsional damper according to the invention in which the local deformations in the ring forming the indentations in the ring advantageously affect only part of the width of the ring.
In U.S. Pat. No. 2,210,074 and as mentioned above, the deformations in the ring cooperate with the openings in the hub disk, these openings corresponding to the housing of springs disposed between the two coaxial parts constituting the torsional damper, which means that the position of these deformations on the rings is necessarily related to that of the openings on the hub disk.
This is not the case in the torsional damper according to the invention, in which the hub disk is advantageously protected, the ring being able to act thereupon if required at a point circumferentially separated from the spring housings, and therefor at a point of the hub disk where it is not radially weakened by said housings.
Other objects and advantages will appear from the following description of an example of the invention, when considered in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.